Week 4 Challenge

Aim:

1. To design the given abutment foundation as per IRC 6 loads. optimize the design as per irc 112.
2. To detail the steel in shallow foundation for abutment.
3. To explain how a shallow foundation in terms of stability,designing,construction different in flyover and in river bridge.

Introduction: Abutment is given of RCC wall type, width deck width 12m and carriage way width 9m and footpath on right side of width 1.5m. Assume height of abutment – 6 meters. and manually calculate the reaction on the bearings from superstructure considering below transverse sections.

Procedure:

Given data - C/c bearing = 13.4m

C/c expansion joint = 14.4m

High flood level = 229.5m

Foundation level = 224.25m

Deck width = 12m

Carriage way width = 9m

Footpath width = 1.5m

Deck slab = 220mm thk.

Crash barrier = 0.5m width

Abutment shaft height = 6m

2. Detail the steel in shallow foundation for abutment.

Ans.

Reinforcement summary for foundation
	Face	Dia mm	Spacing mm		Dia mm	Spacing mm
Heel slab	Bottom	25	200
	Top	25	200	+	25	200
Toe slab	Bottom	25	200	+	25	200
	Top	25	200
Distribution		10	200

3) How a shallow foundation in terms of stability,designing,construction different in flyover and in river bridge?

Ans.

Construction - Before construction firstly site check is done so as to ensure proper planning in terms of avoiding traffic for flyover and retaining water for a river bridge. For excavation machinery requires proper width of structure so for flyover width of existing road is reduced for safe movement of locals and for river bridge if water is present throughout the year then water retaining structures are built like coffer dams.

Flyover is a bridge over another road for allowing traffic without interruption, with its approaches on both sides, So while constructing foundation for a flyover care must be taken that it does not affects exisitng road structure and nearby existing structures. Traffic on the road should be avoided to have ease of construction. For ease of construction precast structural components are installed on site for fast completion.

For a river bridge construction soil quality is checked, if rock is observed near ground level then we go for shallow foundation. During construction flow of water must be diverted or stopped for a while using temperory coffer dams.

Design - For design of river bridge forces like water current, hydrodyanmic forces are taken into consideration when the river is assumed to flow for its highest flood level. Abutments are constructed if ends of bridge have soil to be retained for which wind is not taken into consideration as it is not governing. Bouyancy forces are to be applied on the structure when river water flows. It must be noted that superstucture of river bridge should ne built and designed above free board of highest flood level. Scour level should be considered properly before deciding depth of foundation. It should be designed for low water level, high flood level and span dislodged condition.

For design of flyover and its approaches water forces need not be considered bt wind shoud be considered as it is in open terrain. Depth of foundation is decided based on longitudinal moment of the superstructure. Foundation should also be designed taking into consideration live load on the road above which it is constructed. Temperory structures weight are also to be borne by foundation so approximation of that loading has to be taken into consideration while designing foundation for flyover. It should be designed for full span present condition and span dislodged condition.

Stability - For stability of shallow foundation in flyover proper depth has to be ensured to have enough soil bearing capacity and soil above the foundation to ensure enough soil pressure to counteract uplift.

For stability of shallow foundation in river bridge cases of low water level, high flood level with span present conditions and span disloged conditions should be considered.